The invention relates to a display device comprising at least one compartment which contains an ionizable gas mixture, at least one composite gas of which is a gas of the group constituted by at least hydrogen, said compartment being provided with electrodes for selectively ionizing the ionizable gas during operation, and a getter material in connection with the ionizable gas.
The invention also relates to a method of manufacturing such a display device.
Display devices for displaying monochromatic or color images are, inter alia, plasma-addressed liquid crystal display devices, referred to as PALC displays, preferably of the flat-panel type. PALC displays are used as television and computer displays.
A display device of the type described in the opening paragraph is known from EP-A 0 833 363. The display device of the flat-panel type described in this patent application has a display screen with a pattern of (identical) data storage or display elements and a multitude of compartments. The compartments are filled with an ionizable gas and are provided with electrodes for (selectively) ionizing the ionizable gas during operation. In the known display device, the compartments have the shape of parallel, elongated channels (shaped as a channel plate) which function as selection means for the display device (the plasma-addressed row electrodes). By applying a voltage difference across the electrodes in one of the channels of the channel plate, electrons are emitted (from the cathode), which electrons ionize the ionizable gas while forming a plasma (plasma discharge). When the voltage across the electrodes in one channel is switched off and the gas is deionized, a subsequent channel is switched on. At the display screen side of the display device, the compartments are closed by a (thin) dielectric layer ("microsheet") provided with a layer of an electro-optical material, and further electrodes which function as data electrodes or column electrodes of the display device. The further electrodes are provided on a substrate. The display device is constituted by the assembly of the channel plate with the electrodes and the ionizable gas, the dielectric layer, the layer of the electro-optical material and the further electrodes.
To increase the lifetime of such display devices, decrease the ignition voltage of the plasma and obtain a more rapid extinction of the plasma, several percents of hydrogen are added to an ionizable (basic) gas such as helium in the known display device. The hydrogen gas is supplied in a getter which consists of a ZrVFe alloy in the known display device and is secured by means of a resilient construction in an exhaust box of the compartment.
In practice, the getter is first secured in the exhaust box, whereafter the exhaust box is fritted to the channel plate at approximately 450.degree. C. The frit comprises an organic binder. The getter material is then contaminated with vapor of this binder so that the necessary exhaust time will be longer. To prevent hydrogen from escaping due to excessive temperatures in subsequent thermal treatments and to prevent such a high pressure build-up in the channel plate that the microsheet breaks, the exhaust box is placed in a water-cooled metal capsule during this thermal treatment. Besides the above-mentioned contamination of the getter material, this method has the drawback that the orientation material is not cured or insufficiently cured at the area of the cooled part when using liquid crystal material as an electro-optical material.
More generally, this manufacturing method has the drawback that heating and supplying the getter material with hydrogen results in an unwanted delay in the manufacture of the display device.